The word "cosenage" is spelled with an "s" in the middle, even though it is pronounced with a "z" sound. This may be confusing for some English speakers, but it can be explained through IPA phonetic transcription. The "s" in "cosenage" represents the voiced fricative sound /z/, which is pronounced with vibration of the vocal cords. This is similar to the sound in words like "buzz" and "fuzzy". So, despite the spelling, "cosenage" is pronounced with a "z" sound.
The word "cosenage" originated from the Middle English term "cosynage", which in turn came from the Old French word "cosinage". The Old French term derived from the Late Latin word "consobrinaticum", which translates to "relationship by a mother's sister's child". The root of this word is "consobrinus", meaning "mother's sister's child" or "cousin". Over time, "cosinage" transitioned into "cosenage" in Middle English, referring specifically to the fraudulent practices of cousining or cheating.